This invention relates to a rotary type internal combustion engine wherein the cross-sectional shape of the internal wall of the housing has a greater part which is approximately elliptical and a smaller part which is circular. A rotor is rotatably fixed in said circular portion and a vane is fitted in a slot which extends diametrically through the center of said rotor. During operation, the interior of the elliptical portion of the housing is divided by said vane into two spaces in order that each induction, compression, ignition and combustion, and exhaustion will be performed twice each time said rotor makes two rotations.